capacitive sensor through 30mm of wood

Hello !

After doing research on the possibility of making invisible buttons under a wooden worktop, I came across an invention by Loxone (company specializing in home automation). The "Touch Surface" is an object that has just been pasted under a work surface (up to 30mm thick) allowing to detect a press on a specific area of the work surface. I would like to do a similar project with my arduino but I can't find a capacitive sensor allowing detection at such a distance (AT42QT1011, MTCH101...). Do you have an idea or a component reference to offer me?

Thanks a lot for your help !! :smiley:

Could you drill part way through the worktop from the bottom to bring the sensors closer to the top surface ?

Ultimately, I would like to install it in my kitchen. It is new and it would bother me to drill it.

The Loxone product can detect up to 3cm. I have set myself the goal of doing the same. Do you think it's difficult to do this ?

Thank you for your quick reply !! :smiley:

Yes, it's difficult, but I think you won't find "better" IC's. You should really study this app note:

Possible - sure. Difficult - you bet. My record is close to half a meter, using Theremin type detection. Ridiculously sensitive (best keep doors closed - that kind of sensitive), it's based on LC oscillators. That AN is talking about 0.5-5 pF changes; the theremin circuits sense changes in the fF (femto Farad) order of magnitude. The main problem with that technique may be directionality - specifically the lack of it.

Go get some TTP223 Touch Sensors and experiment with placing your touch pads under the wooden surface. You will want to use fairly large pads - a few square inches each.


(The tiny terminal at the top right of each board as shown is where you connect your touch pad.)

I've gotten those to work through a few mm of clear plastic; seen reports of a few mm of plywood. Not much hope for 30 mm.

That's why I referred to fairly large pads. Not just the pad on the PCB. :grinning:

There are new sensors available that work on the doppler effect called microwave radar sensors.

These can penetrate non-metal structures and the one I linked to reportedly has and adjustable range of between 0.4 and 32 ft, so quite a range.

We do not use this particular type but many manufactured types are around.

The rcwl-0516 is one such sensor that can be used with the Arduino, works great for motion detection in its general environment.
It's not radar, nor doppler, or whatever those advertisements say. It's actually working at about 6 GHz (so at least it is in the microwave part of the spectrum) and it looks for changes in interference patterns. The large range and full surround sensitivity makes these sensors useless as touch/proximity sensor as the OP is looking for.